This invention relates to an apparatus for detecting the resonant frequency of a bone and, in particular, although not exclusively, to the resonant frequency of human long bones such as the tibia, femur, radius and ulna.
A need exists to determine the fracture repair of bones and the current medical practice of using X-ray methods requires expert interpretation and normally takes eight weeks to assess a fracture.
It is known that bones have a mechanical resonant frequency and that by striking a bone to set up a frequency therein the resonant frequency may be determined and all bones have such resonant frequencies.
Two main factories determine the resonant frequency of a bone and these are the bones stiffness and mass. The stiffness of a bone when it is repairing after a fracture is less than that of the rest of the bone so that the stiffness of a repairing bone and hence the resonant frequency of that bone are reduced in comparison with the persons non-fractured bone. However, as the bone heals, the stiffness approaches that of an unfractured bone and so the resonant frequency also reverts to its normal value. It is known that a callous eventually forms at the fracture site which provides the bone with a greater mass than the unfractured bone and so the final resonant frequency is slightly lower than that of the original unfractured bone.